Recently, communications systems have advanced for both personal and business uses. The concept of a "wired nation" connected by an "information highway" has come closer to reality. New communications techniques using fiber optic communications (e.g., fiber-to-feeder, fiber-to-home or the like) allow the transmission of larger quantities of data from point to point, making possible such heretofore impractical concepts as video-on-demand (VOD) or picturephone.
However, with the increased reliance upon these communications systems for both business and recreational use comes the increased inconvenience associated with the interruption of such services. Traditional techniques for stringing wires or fiber optic cable from poles have proven too susceptible to storm and wind damage and in addition are aesthetically displeasing. The traditional solution of cable burial has proven susceptible to other hazards--the weekend gardener or the construction worker accidently severing communications lines during excavation activities. In addition, in prior art burial techniques, it has been difficult to bury additional cables to modify or upgrade a communications network without disturbing the existing buried cables.
One solution to these aforementioned problems has been to place underground wires or cables in a protective conduit or duct. The duct is relatively water-tight or water resistant and is robust enough to withstand at least minor disturbances. Generally, the duct is of such a diameter that additional cables or wires may be "snaked" through at a later date if it is desired to add additional cables.
As shown in FIG. 1A, conduit or duct 118 is typically used to connect service pedestals 116, 117 in residential housing subdivisions and in commercial building applications. Utility pedestals 116 and 117 are pedestals which are well known in the art and serve as access points for selected wires or cables carried within a duct system. In addition, pedestals 116 and 117 may carry selected electronic equipment (line amplifiers or the like). Pedestals 116 and 117 are further connected to other portions of the communications system by duct portions 119 and 120 which in turn may be connected to further pedestals or the like.
Duct 118 may be, for example, four inch type "C" duct or duct made of polyvinyl chloride (PVC) to telephone company specifications. Other types of materials may also be used including fire retardant plastics and conceivably, metal. Duct 118 may be used to house fiber optic or coaxial cables or copper conductors. In residential applications, duct 118 is run between service pedestals 116,117 in a subdivision.
Service drops to subscriber's residences 110-115 are run by smaller interducts 121-126 from service pedestals 116,117. The number of interducts may be varied depending upon the number of subscribers to be connected to the communication system. Here, for the sake of illustration, six such interducts are shown. The term "subscriber" as used in the present application means an individual or household connected to the communications system, however, the term "subscriber" could also refer to a business or other enterprise.
Running interducts 121-126 from pedestals 116,117 has several practical disadvantages. In new home construction, for example, utility lines are often laid before construction begins. Thus, if interducts 121-126 are installed prior to construction, there is a hazard that they may become damaged during the construction process. Between the time of installation of interducts 121-126 and construction of residences 110-115, locations and layout of residences 110-115 may change, forcing the utility company to return to the site to dig up existing interducts 121-126 and install new ones. Since interducts 121-126 are run to pedestals 116,117, an entire trench must be dug back to pedestals 116,117, along duct 118, to remove the old interduct and a new trench dug to install a new one. This technique involves extensive digging and introduces the risk of damage to duct 118.
In commercial applications, it is often desirable to use fire resistant duct to enclose communications cables. In many commercial facilities, such as offices, the locations of individual offices and data facilities (telephone, computer rooms and the like) are often determined after the shell of the building has been constructed and the utilities installed. Further, office spaces are subject to periodic rearrangement. It is difficult to provide suitable access points in the duct system that anticipate all possible future needs without escalating costs dramatically. Cutting into an existing duct is dangerous, as the signal cables within the duct accidentally may be cut or damaged during the process.
One approach to solving this problem is to delay installation of interducts 121-126 until the corresponding subscriber home (or in a commercial application, office) is completed. This approach, however, still requires that a long trench be dug from the pedestal to the home after the home is completed. FIG. 1B shows a more direct technique for installing interducts which avoids the necessity of digging a long trench. For example, once subscriber home 113 has been located, interduct 134 is tapped off from duct 118 directly, rather than from pedestal 116 or 117. Thus, as an example, for subscriber home 113, a trench need only be dug directly from subscriber home 113 to duct 118 to house interduct 134. This approach uses less duct, involves less digging, and does not disturb buried duct 118 as much as the technique shown in FIG. 1A. The approach shown in FIG. 1B, however, requires that a safe, economical and easy to use technique be available to tap-off the existing duct 118.
FIG. 2 shows an apparatus disclosed in Moran U.S. Pat. No. 4,342,475, issued Aug. 3, 1982. A technique is illustrated for tapping off a multiple bore conduit 10 with connection 28 comprising a saddle element 31 coupled to a sleeve element 29 or 30 to feed a tubular duct 11. A separate bore is provided for each wire or bundle of wires. The multi-bore duct has obvious disadvantages in that it can only carry a limited number of wires. Further, such a duct is not easily fabricated. As a result, the industry today has standardized on a so-called "C" duct, made of polyvinylchloride (PVC), typically four inches in diameter. A number of wires or cables can be carried through one "C" duct, and additional wires can be added at a later time by "snaking" the wires through the duct from pedestal to pedestal.
Application of the tap-off technique of Moran to a "C" duct presents difficulties in breaching the duct in order to form the tap-off point. Cutting into a duct always risks cutting a cable or wire within the duct. Splicing cut wires within a duct, typically at the bottom of an open trench, is both messy and difficult. With the introduction of fiber-optic cable the problem is compounded further. Fiber-optic cables are difficult and expensive to splice, and a splice may introduce a signal loss into the fiber optic signal path. In many instances, a cable sheath can be nicked or abraded during the cutting process without notice by the installer. Over a period of time, such nicks can allow moisture to enter, causing corrosion, and eventually failure of the cable. The installer must then return to the site and dig again to make necessary repairs, further disturbing duct 118.
The duct tap-off technique of Moran also poses the hazard of introducing contaminants into the duct in the form of chips, dust, etc. created by the cutting process. Chips and duct can accumulate in the duct and abrade or nick cables being snaked through a duct. Such contaminants can cause friction between a cable being snaked through a duct and existing cables, making the snaking process more difficult, especially in long runs. This contamination problem would exist in like manner in joining plumbing pipes where such contaminants can clog or damage fittings, valves, or the like.
The tap-off device of Moran, being made up of a multi-piece saddle and tap, can be difficult to install when working at the bottom of an open trench. Both pieces must be properly aligned and set in place while adhesive or clamping devices are used. The multi-piece construction increases costs, as the pieces themselves are expensive to manufacture, and an inventory of the various types of tap-offs (corner, side, top) must be maintained. Prior art PVC plumbing fittings are also expensive, with a simple street ell or tee fitting costing as much as a ten foot length of pipe.
Thus, it is an object of the present invention to provide a technique for tapping off a duct or pipe without endangering or contaminating the contents of that duct or pipe.
It is a further object of the present invention to provide a technique for tapping off a duct or pipe which can be easily and quickly implemented in a working environment.
It is an even further object of the present invention to provide a effective, low cost technique for tapping off a duct or pipe.